Chemistry December 2001 Vol 50/4 []

CONTENTS & ABSTRACTS

InEnglish. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.

Chemistry



Volume 50 No. 4December 2001



Fifty years of publications on chemistry in the Proceedingsof the Estonian Academy of Sciences; 203–204

(full article in PDF format)

Ülo LILLE

Xylidine-pollutedgroundwater purification. Adsorption experiments and breakthrough calculations; 205–216

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Janek REINIK, Andres VIIROJA, and Juha KALLAS

Abstract. 2,4-Xylidine is acarcinogenic component originating from missile fuel, and it often dominates inpolluted groundwater in the areas of abandoned Soviet missile bases in EasternEurope. One of the possible processes for its removal is adsorption ontogranulated activated carbon. However, the corresponding equilibriumrelationships as well as information on the process kinetics are not available.In this work Langmuir’s and Freundlich’s isotherm parameters were obtained frombatch adsorption equilibrium tests. Initial concentration of 2,4-xylidine wasvaried in the range of 200–300 mg/L in the experiments. The solid phasediffusion coefficient was obtained from the batch kinetic runs. Thebreakthrough curves were measured during dynamic experiments in two packed bedcolumns with diameters of 16 and 26 mm. The obtained experimental curveswere compared to those calculated by the Thomas and Rice methods. In some casesa satisfactory fit was achieved, but in several cases more advanced modellingmethods should be used for better prediction of the xylidine-contaminatedgroundwater breakthrough profiles in a packed bed reactor.

Key words: 2,4-xylidine,adsorption isotherm, kinetics, dynamics, packed bed adsorber design,breakthrough curves.

Determinationof peppermint and orange aroma compounds in food and beverages; 217–225

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Anne ORAV and Jüri KANN

Abstract. Qualitative andquantitative variation of volatile aroma compounds in different foods andbeverages containing peppermint and orange aroma was studied using thesimultaneous distillation and extraction micromethod for isolating the aromafraction and capillary gas chromatography for analysing the extracts. Inpeppermint aroma 41 constituents and in orange aroma 22 compounds wereidentified. The yields of aroma fractions from different materials varied from0.2 up to 24 mg/g (peppermint) and from 0.03 up to 2 mg/g (orange).

Key words: Mentha piperita, Citrus sinensis, aroma compounds, tea, juice, chewing-gum, sweets,SDE, capillary GC.

Behaviourof 1-butoxy-9-tetradecyne in superbasic MEDA/EDA media; 226–228

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Anton KOTLJAROV, Artur JÕGI, Sirje MÄEORG, and Uno MÄEORG

Abstract. The first example of theisomerization of a non-propargylic alkoxyalkyne, 1-butoxy-9-tetradecyne, insuperbasic media MEDA/EDA (M = Li, Na) is presented. The extentof the competitive elimination reaction and the influence of the type of metalin superbase on the composition of product were determined.

Key words: alkoxyalkyne,triple bond, isomerization, superbase, MEDA.

Changesin membrane fluidity during the micelle formation determine the efficiency ofthe solubilization of muscarinic receptors; 229–240

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Sergei KOPANCHUK and Ago RINKEN

Abstract. The influence of variousconcentrations of 15 detergents at different temperatures on the fluidity ofmembranes was analysed by fluorescence anisotropy of inserted1,6-diphenyl-1,3,5-hexatriene in rat cortical and Sf9 cell membranes. Comparison of the obtained data with theabilities of the detergents to solubilize muscarinic receptor subtypesindicated that not only the fluidity of the micelles formed but also themicelle formation process, the lipid/protein ratio, and presence of sterolshave significant influence on the efficiency of the solubilization of mAChR.Digitonin seems to exploit efficiently all these factors by its biphasicmodulatory effect on membrane fluidity during the receptor solubilization.

Key words: membrane fluidity, solubilization, detergents, muscarinicreceptors, rat cerebral cortex, digitonin, cholesterol.

Phosphorus–carbondiad tautomerism in phosphonium compounds. Theoretical study; 241–253

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Peeter BURK, Uldo MÖLDER, and Kaido TÄMM

Abstract. Phosphorus–carbon diad tautomerism was studied in phosphoniumcompounds with such strong electron acceptor substituents as cyano-, nitro-,fluorosulphonyl-, and trifluoromethyl­sulphonyl groups using semiempirical, ab initio, and DFT methods. It was shownthat in the gas phase all studied monosubstituted species are in the phosphorylform and no enol forms should be detectable. In contrast, for doublysubstituted compounds enol forms should be well detectable and in some caseseven predominant. Comparison of different calculation methods indicated that ab initio (HF/6-31 + G*) andDFT (B3LYP/6-311 + G**) calculations give close results. Both appliedsemiempirical methods (PM3 and MNDO/d) seem to overestimate strongly thestability of the enol form. It was also found that the MNDO/d method givesunrealistic results for compounds containing both hypervalent phosphorus andsulphur.

Key words: enolization,phosphoryl group, calculation, PM3, MNDO/d, DFT.



Contents of volume 50; 254–256